I would greatly appreciate here if a chemist/microbiologist/geneticist could explain how does this work without a model of the human immune system? The article

I would greatly appreciate here if a chemist/microbiologist/geneticist could explain how does this work without a model of the human immune system? The article describes the process as follows: Step 1. Somehow train an AI to distinguish compounds that work vs those that don't work. Step 2. Train another AI to somehow select candidates from trillions of possible compounds that work. Step 3. ??? Step 4. Test vaccine.